A series of CuIn1-xGaxSe2 solar cells with varied Ga content (O <= x <= 1) was prepared using a three-stage co-evaporation process. The grain sizes of these devices vary with gallium content, exhibiting a maximum for approximately x=0.2, which does not coincide with the maximum of the solar conversion efficiency observed between 0.340.7) an additional defect appears. An equivalent circuit model describing a parallel connection of bulk and grain boundary capacitors allows us to conclude that the detected shallow defect is not predominantly located at the grain boundaries. (C) 2008 Elsevier B.V. All rights reserved.